Acoustical mine firing control system



Jan. 16, 1962 H. H. HALL 3,016,829

ACOUSTICAL MINE FIRING CONTROL SYSTEM Filed Feb. 10, 1945 4 SheetsSheet 1 Jan. 16, 1962 H. H. HALL ACOUSTICAL MINE FIRING CONTROL SYSTEM 4 Sheets-Sheet 2 Filed Feb. 10. 1945 jwum vbob H. H. HALL m9 2 E B 2w mm m lm l m 4 Sheets-Sheet 3 R3 is:

H. H. HALL ACOUSTICAL MINE FIRING CONTROL SYSTEM Jan. 16, 1962 7 Filed Feb. 10, 1945 LIMITING POTENTIAL Fl l I SECONDS TRELAY ARMATURE MOVES TOWARD CONTACT C o mmmzuozOo zO JShZMhOQ mmuuxu 1K" T JT M m lil m M w $285:

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ACOUSTICAL MINE FIRING CONTROL SYSTEM Filed Feb. 10, 1945 4 Sheets-Sheet 4 Locus OF Tl a T2 (D g \DURING SHIP APPROACH 0 Y/ O U. U)

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3,016,829 ACOUSTICAL MINE FIRING CONTROL SYSTEM Harry H. Hall, United States Navy, Washington, D.C. Filed Feb. 10, 1945, Ser. No. 577,249 19 Claims. (Cl. IM -1S) (Granted under Title 35, US. Code (1952), sec. 266) This invention relates to mine firing control systems and more particularly to an acoustic mine firing control system for underwater mines wherein the system operates to detonate and explode the mine associated therewith when vibrations or pulsations of a predetermined character are transmitted through the surrounding waterfront sound emitting bodies such as surface vessels, submarines, or the like, and the system operates to prevent a firing of the mine by detonation of neighboring charges and the reverberations ensuing therefrom.

. In certain of the prior art systems, electric contact actuating apparatus comprising a plurality of contacts is employed wherein a first pair of contacts is adapted to be actutaed by sound waves of a predetermined character such, for example, as those produced by a vessel in motion, thereby to control the operation of a mine firing circuit, and a second pair of contacts isadapted to be actuated by sound waves of a different character, such, for example, as explosion waves, thereby to prevent the first pairlof contacts from controlling the firing circuit when such difierent sound waves or signals are received. Thus, by this arrangement, a certain measure of protection or discrimination against such different signals is provided. In accordance with such an arrangement, a time delay device is usually employed to continue the control provided'by the second pair of contacts for a predetermined interval of time, thereby to render the firing circuit inoperative until the aforesaid difierent signals have died out in the acoustic field or Zone of receptivity of the mine.

In he arrangement of the present invention, an acoustic mine firing control system is provided which'possesses all the advantages of the prior art systems and which contemplates a high degree of control of a mine firing circuit and of a circuit adapted to sterilize the firing circuit for a'predetermined interval of time in accordance witlrthe character of sound signals transmitted through the surrounding water. Moreovensuch high degree of control over said two circuits is accomplished by the inclusion of fewer and less complicated intermediate devices and elements, thereby providing a system which has as its desirable features simplicity, compactness and efiiciency.

In accordance with a preferred embodiment of the instant invention, an acoustic tickler is employedcomprising a pair of contacts adapted to vibrate as sound signals of a predetermined character such, for example, as those received from a vessel moving with respect to the mine, impinge against the surface of the tickler. As the contacts vibrate in response to such signals, current is caused to flow intermittently through a charging and a discharge circuit of a condenser. included in both the charging and discharge circuits of the condenser and is caused to close a firstcircuit adapted to fire the mine when the current flowing through the discharge circuit reaches a predetermined average value and flows therethrough for a predetermined period of time.

When a signal of a different character is received by the tickler such, for example, as a countermine shock corresponding to a sound signal of abnormally'high intensity, and the contacts of the tickler are forced open for a predetermined interval of time, a surge of current of sufficient magnitude is caused to flow through the An electro-responsive device is' vessel. The second curve, shown in solid outline, definescharging circuit of the condenser, and hence through the eiectro responsive device, for a sufficient time to cause the electro-respcnsive device to close a second circuit which is adapted to sterilize the minefor a predetermined period of time.

An object of the present invention is to provide 'a new and improved acoustic mine firing control system for nderwater mines in which the system operates to detonate and explode the mine when sound signals of predetermined character are transmitted through the surrounding water.

Another object is to provide a new vand improved mine firing control system suitable for'use with an acoustic tickler and in which the system operates to prevent a firing of the mine when signals of different character are transmitted through the surrounding water. .2

Another object is to provide a new. and improved acoustic mine firing system for marine mines in which the system operates to prevent firing of the mine when signals of predetermined character and of diiterent character are transmitted concurrently through the surround-. ing water.

Another object is the provision of ajnew and improved mine firing control system in which a sound re.- sponsive device effects firing of the mine upon the lapse of a period of time beginning with the reception of sound waves of a predetermined character by'the sound responsive device.

A further object of the instant invention is to provide a mine firing control system in'which a pair of contacts are adaptedto be opened and closed intermittently in response to sound signals transmitted throughan elastic medium and in which intermediate devices are adapted to produce a firing actuation of the system only when the ratio of the closed interval of the contacts to the open interval thereof falls. within a predetermined range of ratios.

A further object is to provide an' acoustic mine firingr control system which operates to detonate and explode a mine when sound signals received thereby reach a predetermined degree of strength and fall within a predetermined frequency band.

A still further object is to provide an acoustic mine: firing control system which is simple in operation, compact in structure, reliable in service and economical to manufacture.

Additional objects and advantages of the invention not specifically set forth heretofore, and which are inherent in the novel selection and arrangement of the elements comprising the invention, will become more clearly apparent as the description proceeds, reference being made; to the accompanying drawings wherein: Y

FIG. 1 is a view, partially broken away and partiall in section, of a mine suitable for use with the system of the present invention; a

FIG. 2 shows in diagrammatic form a complete system suitable for use with the mine of FIG. 1;

FIG. 3 shows in diagrammatic form the respective charging and discharging circuits of the condenser shown in FIG. 2;

FIG. 4 shows in graphic form the variation in potential produced across the condenser of FIG. 2 as the contacts of the acoustic tickler are caused to be opened and closed at regular intervals:

FIG. 5 shows in graphic form the direction and magnitude of the current caused to flow through the relay coil as the tickler contacts open and close at regular intervals;

FIG. 6 shows two curves, the first of which is drawn in dashed outline and illustrates the average manner in which the tickler contacts respond to an approaching 3 the manner in which the tickler contacts must respond to an approaching vessel in order to cause a firing actuation of the system of FIG. 2; and,

FIG. 7 shows in graphic form the deflection of the relay armature of FIG. 2 in accordance with the direction, magnitude and time of current flow through the relay coil.

Referring now to the drawings for a more complete understanding of the invention, wherein like reference characters refer to like parts throughout the several views, and more particularly to FIG. 1 thereof, the numeral 10 generally designates an underwater mine adapted to be launched into a body of water and to come to rest on the bed thereof. The mine comprises an outer casing 11 generally of cylindrical configuration and having a reduced end portion to which fins 12 or the like are secured to steer or guide the mine in its path of travel.

The casing 11 is divided internally at the reduced end portion thereof by a bulkhead 13 which supports a well 14 for a purpose hereinafter disclosed. The casing 11 is also provided with inwardly extending wells. 15 and 16 from which extend respectively, tubes or ducts 17 and 18 to the bulkhead 13. The casing is further provided with a well 19 in which a percussion detonator may be inserted, if desired, when the mine 10 is to be used for purposes other than those disclosed herein. Accordingly, for purposes herein disclosed, the well 19 is sealed as by the plug 21. I

The remaining space within the main portion of the casing 11 is filled with an explosive charge 22 of TNT or the like sufiicient to destroy or damage a vessel and to impart a negative degree of buoyancy to the mine whereby the mine is caused to sink through the water and to come to rest on the bed thereof. The explosive charge conveniently may be admitted'to the casing by way of a suitable watertight filler opening 23.

A booster charge 24 and the extender mechanism 25 usually associated therewith are arranged within the well 15 in water-tight relation therein. The extender mechanism carries an electro-responsive detonator 26 for igniting the booster charge 24 and is adapted to move the detonator into operative engagement with the booster charge when the mine reaches a predetermined depth of submergence in the water, as is well known in the art to which the invention appertains. The leads 27 of the detonator comprise a cable 28 which is extended through the duct 17 to the reduced end portion of the casing 11.

Arranged within the Well 16 in watertight relation therewith, is a clock mechanism 29 of any type suitable for the purpose such, for'example, as the clock mechanism described and claimed in the copending application of James B. Glennon et al. for Firing Mechanism for Submarine Mine, Serial No. 395,230, filed May 26, 1941, now PatentNo. 2,905,088, and adapted to complete certain circuits of the electrical system within predetermined intervals of time after the mine has been launched within the water, as will more clearly appear as the description proceeds. For this purpose, a multi-conductor cable 31 connected to contacts comprising the clock mechanism is extended through the duct 18 into the reduced end portion of the casing.

The well 14 serves as a housing and support for a battery, hereinafter referred to as BA, the battery being clamped within the housing against a resilient support 32 therein by means of a retaining ring 33 secured to the bulkhead as by a plurality of studs 34. The battery BA is arranged to supply electrical energy to a firing control mechanism 35 by way of a multi-conductor cable 36 when the aforesaid certain circuits have been closed by the clock mechanism 29 as explained in the foregoing.

The mechanism 35 is supported onthe studs 34 by means of a plurality of flexible spacer plates 37, which plates may be formed of any suitable material such, for example, as wood, the plates being supported on the studs and shaped to conform to the end portions of the mechanism. The free end portions of the studs 34 extend through and are supported by the plate 38, which plate is shaped to conform slideably with the inner surface of the casing 11. The projecting portions of the studs are threaded to receive a plurality of nuts 39 whereby the mechanism 35 may be clamped between the plates 37 when the nuts are drawn up tight against the slideable plate 38.

The reduced end portion of the mine casing, at the open end thereof, carries a ring member 41 which is secured to the casing as by welding or otherwise suitably secured thereto. A dish-shaped cover 42 is secured to the member 41 in watertight relation therewith as by a plurality of screws 43 carried by a flanged portion 44 of the cover. The cover is provided with a central opening for receiving a sound'responsive device 45, hereinafter referred to as an acoustic tickler. The tickler 45 is provided with a circular base 46 by means of which the tickler is secured, as by a plurality of screws 47, to the cover. It will be understood that the tickler 45 may be of any type suitable for the purpose such, for example,

as the tickler described and'claimed in the copending application of Harvey C. Hayes et al. for Detecting Device, Serial -No. 412,112, now Patent No. 2,396,699, filed September 24, 1941, and comprising, generally a flexible diaphragm adapted to be vibrated when pressure signals impinge against the surface thereof and a pair of normally closed contacts operatively connected to the diaphragm in such a manner as to cause the contacts to vibrate concurrently with the vibration of the diaphragm.

FIG. 2 shows in diagrammatic form a complete system suitable for use with the mine of FIG. 1 and comprising an arming clock 29 heretofore described as adapted to close a plurality of circuits in predetermined sequential order when a predetermined interval of time has elapsed after the mine is launched into a body of water, an electro-responsive detonator 26, and an acoustic tickler 45 including the normally closed contacts 48 and 49. A battery BA is arranged to supply energy to the condenser C1 and to the operating magnet OM of the relay R when contacts 48 and 49 are disengaged. The relay R is a sensitive polarized relay comprising an armature 51 adapted to be moved into engagement with a first contact associated with the relay R, hereinafter referred to as the firing contact f when current of predetermined magnitude flows for a sufficient time in one direction through the coil or operating magnet of the relay, the armature 51 also being adapted to move into engagement with a second contact included on the relay, hereinafter referred to as the countermining contact 0, when current of predetermined magnitude flows for a sufficient time in the opposite direction through the operating magnet of the relay.

Another battery, BAl, is arranged to supply energy to a thermal delay switch 52 when the armature 51 of relay R moves into engagement with contact 0 thereof. The switch 52 comprises a movable armature 53, of the bimetallic type, normally engaging a cold contact 54 and adapted gradually to move into engagement with a hot contact 55 when current flows through a meter coil 56 for a sulficient time, the armature gradually returning to its normal position in engagement with the cold contact 54, after current ceases to flow through the coil 56.

A more detailed description of the operation of'the circuit shown in FIG. 2 will hereinafter be given.

FIG. 3 shows in diagrammatic form that portion of FIG. 2 which includes the respective charging and dis charging circuits of the condenser C1. The resistors R1, R2 and R3 are connected across battery BA to form a voltage divider circuit such that when no sound waves are reacting upon the tickler-'45 and, therefore, contacts 48 and 49 remain in engagement with each other, the

circuits are in a state of stablcequilibrium and a poten- ,5 tial exists across condenser C1 of a value determined by the resistors R1, R2 and R3, the value being approximately three-eighths of the output voltage of battery BA. The voltage appearing across C1 when the circuits are in a state of stable equilibrium will hereinafter be referred to as the quiescent voltage of condenser C.

As is well known in the art, the operation of a tickler of the type employed herein in response to pressure impulses or sound Waves impinging against the diaphragm thereof causes the contacts associated therewith to be vibrated, the frequency of this vibration being determined by the frequency of the sound signals causing the vibration and the average length of the open and closed time intervals of thev contacts being determined by the strength or intensity of the signals being received.

Assuming that the thickler 45, FIG. 3, is set into eration, a brief description of the operation of the charging and discharging circuits of condenser C1 will be given. As the tickler is set into operation, contact 48 thereof is disengaged from contact 49 thereof for an interval of timeihereinafter referred to as T1, the open time. When this occurs, current is caused to fiow from the positive terminal of battery BA over conductor 57, through the charging resistor R1, conductor 58, through condenser C1, conductor 59, operating magnet OM of relay R, conductor 61, resistor R3, conductor 62, from whence the circuit is completed to the negative terminal .of battery BA, thereby increasing the potential across condenser C1 in a well known manner.

At the end of the open time T1, contacts 48 and 49 move into engagement with each other for an interval of time, hereinafter referred to as T2, the closed time. Vihen this occurs, condenser C1 is short-circuited and current is caused to flow from the positive plate of condenser C1, over conductor 58, discharge resistor R2, contacts 48 and 49 of the tickler 45, conductor 61 operating magnet OM of relay R, conductor 59 and thence to the negative plate of condenser C1, thereby causing the potential across C1 to be decreased. It is important to note at this point, that thecondenser charging current, which flows during the open time T1, passes through theopcrating magnet OM in one direction While the discharge current thereof, which flows during the closed time T2, passes through OM in the opposite direction.

In view of the foregoing description of the operation of the charging and discharging circuits of condenser C1, it is apparent that as the contacts 48 and 49 of the tickler 45 continue to vibrate, the potential across C1 will increase during each of the contacts open time T1, thereafter decreasing during the contacts closed time T2. With reference to 'FIG. 4 of the drawings, this variation in potential across C2 will be described in more detail with a view toward showing that an increase or decrease in the potential across Cl depends upon the values of the open time T1 of the contacts and the closed time T2 thereof, respectively, and that there exists, during a continuous vibration of contacts 48 and 49, a limiting value of potential of condenser C1.

In FIG. 4, a curve of the variation in voltage of condenser Cl versus time in secondsis plotted in which the contacts 48 and 49 of the tickler 45 are assumed to open and close at regular intervals T1 and T2. As is well known in the art, any circuit containing resistance and capacitance such, for example, as the charging or discharging circuit of condenser 01, FIG. 3, is subject to a transient period when the amount of energy stored therein is varied. Moreover, transients in such a circuit, whether of voltage or current, are represented by exponential functions of time with a negative exponent.

Referring to the charging circuit of condenser C1, FIG. 3, let:

E=potential of battery BA Eqr-equiescent voltage of condenser C1=.approx. 5 volts t llCf idt=Ec=excess potential on C1 over Eg gained 0 after the contacts 48 and 49 have been open for a time t The fundamental differential equation for the circuit where i=instantaneous value of current at a time I iRl=instantaneous value of voltage across R1 To obtainin expression for current as a function of time, differentiate Equation 1 with respect to t,

@Qfivfi or iRl=(E- apea where I e=Naperian base then Referring now to FIG. 4, let

Substituting the above nomenclature in Equation (3),

XO=YI +XOA Where v V A -a.T1

where and T1=0.05 second Thus, Equation 4 gives an expression for the instantaneous value of voltage appearing across condenser C1 at the end of the first open time interval Tl. Thefactor A employed in Equation 4 is definedas a proportionality factor, the value of which is dependent upon the interval of time T1 since R1 and C are constants, therefore, it follows that Equation 4 gives the value of voltage appearing across condenser C1 at any instant during the first open interval T1 by substituting T for T1.

In a similar manner, an expression for the instantaneous value of condenser voltage at the end of the closed interval T2, may be developed, such an expression taking the form of 7 X1 =X0- Y1B (5 Where and 1 ine T2=0.20 second The factor B is also a proportionality factor the value of which is dependent upon the value of T2 and, therefore, the value of condenser voltage at any instant during the first closed interval T2 may be expressed as YlB if T is substituted for T2.

Then

But the sum of a power series is In accordance with Equation 6, it is apparent that the potential Y of condenser C1 approaches a limiting value as the result of a continued series of opening and closing intervals of lengths T1 and T2, respectively. As the contacts initially open, the potential on the condenser C1 is the quiescent potential and is ineffective to prevent a relatively large flow of current through the condenser, hence the voltage of the condenser is increased somewhat by such a flow of current. At the end of the first open time, the potential Y is not sufficiently large to cause a large amount of current to flow through the discharge circuit of condenser C1, hence the decrease in Y during this closed interval is small. Under these conditions of a relatively large increase in potential Y during the first opening and of a relatively small decreaseof Y during the next successive closing, the net potential axisting across C1 has increased over the quiescent potential thereof. However, as the contacts continue to vibrate, a condition is reached whereby any increase in Y during the open time is relatively small due to previous successive increases in Y which will oppose the charging potential, and as the closed interval begins, the potential Y will be sufliciently large to cause a large flow of current through Cls discharge circuit and thereby cause Y to decrease in value an amount equal to that increase gained through the last'open interval. It should now be apparent that during further vibration, of the contacts, the condenser potential remains substantially constant, thus reaching the limiting potential as heretofore defined.

Furthermore, with reference to Equation 6, it is apparent that the limiting value of Y is determined by the average ratio of the closed intervals to the open intervals. If such a ratio is increased, the limiting potential will increase and vice-versa.

The currents which will flow through the operating magnet OM of the relay R are proportional to the excess potential Y of condenser C1 when the tickler contacts are closed and to the difference of .potential X between the battery and condenser when the tickler contacts are open. As heretofore described, these currents flow in opposite directions through the relay and tend to swing the armature 51 thereof toward the 0 contact when the tickler contacts are open and toward the f contact when the tickler contacts are closed.

These conditions are shown in FIG. 5 of the drawings and, with reference thereto, it will be noted that the horizontal time axis thereof corresponds with the horizontal time axis of FIG. 4, and that those portions of the current curve lying above this axis denote current flowing through the charging circuit of condenser C1 during the time interval T1 while those portions lying below the time axis denote current flow through the discharge path of condenser Cl during the time interval T2. At the initial opening of the tickler contacts it is seen that the current 10 caused to flow through the charging circuit of C1 equals where L=the effective resistance of the charging circuit, and the instant thereafter that the contacts close, current is caused to flow through the discharge path of condenser C1 of a value equal to where K=the effective resistance of the circuit of FIG. 3 when the tickler contacts are closed.

As the tickler contacts continue to open and close at regular intervals T1 and T2, the current caused to fiow through the charging circuit of C1 will become smaller progressively for the reason that the voltage effecting the current flow decreases progressively. However, the current caused to flow through the discharge circuit of Cl becomes larger progressively since the voltage Y increases progressively. This cycle of operations continues until the value of the discharge current becomes equal to the amount of current which must necessarily flow through the relay R in order to cause the armature 51 of relay R to move into engagement with contact 1 thereof. This condition is represented by the intersection of the current curve with the horizontal dashed line FIG. 5 which represents graphically the value of current necessary to close contact I.

By reference again to FIG. 4 and FIG. 5, it is seen that Yn =peak current for a voltage of Xn ;g=peak current for a voltage of Yn and in the limiting case For the special case in which Ice is taken as just sufiicient to close contact f the expression (7) can be rewritten.

- lA L =I =If=cnrrent to close contact f By substituting the values of A and B into Equation -8 T1 may be separated from T2 by giving the relation a 112 m( k) T2 1o,,e f-l- 1 ta This relation is plotted in solid outline in FIG. 6 of the drawings by assuming various values of T1 and solving for T2. This ratio 01'- threshold curve divides the area between the axes into :two regions, one region being located between the curve and the horizontal axis whereby a ratio of T2 to T1 falling within this region will allow enough current to flow through relay R and eventually close the 7 contact of the relay during further vibration of the contacts. The second region is located between the curve and the vertical axis and a ratio of T2 to T1 falling therein will not cause enough .current to flow through relay R to close contact 1 thereof.

The vertical line drawn at T1 0.127 second, FIG. 6, corresponds to the value of T1 at which contact 9 will be closed when the contacts of the tickler close at the end of the first open interval. It will be understood, however, that in the complete circuit, FIG. 2, a pulse of this duration would initiate'an antiacountermining cycle, the operation of which willbe described hereinafter.

With further reference to FIG. 6 of the drawings, there is shown therein a dashed outline curve which represents hypothetically the manner in which the contacts respond to a ship passing over the mine. When the ship is approaching, the tickler contacts remainlargely closed, opening on theaverage for infrequent intervals corresponding to long T2 and short T1 As the ship nears the mine and the intensity of the shipsisound reaching the tickler increases, the contacts open on the average for relatively longer and more frequent intervals corresponding to points on the dashed curve nearer the threshold curve, and as the ship passes over the mine the average relation .of the intervals T1 and T2 becomes such as to cross the threshold curve, thereby closing contact f in a manner heretofore described.

It will be noted that the periodic opening and closing of the tickler contacts is caused by modulation of a ships sound by the ships propeller blade frequency and that Without such modulation a sound of gradually increasing intensity will cause the tickler contacts to open at a certain threshold level andremain open for a period of time sufhcient in length to effect the operation of an 'anti-countermining cycle, whereby a certain measure of discrimination against sound signals not intended to fire the mine associated with the system of the instant invention is provided.

In the foregoing discussions of the movement of armature 51 of relay R into engagement with the 1 contact, the effects of the inertia and inductance of the armature have been disregarded. However, this was done for the reason that the armature lag behind the charge and discharge current of condenser C1 resulting from such effects is of slight importance only since the average position of the armature will follow the average current, particularly when T1 and T2 are relatively short. Advantage is taken of the inertia of the relay armature, however, in the anti-countermining operation of the systern. In FIG. 7 have been plotted a current pulse, solid line, received when the contacts of the tickler have been open for a relatively long time as by the shock wave from a countermining explosion and the resulting motion of the relay armature, dashed curve. It is apparent from the dashed curves that if the contacts remain open for a comparatively long interval of time, the relay armature wiil eventually attain a deflection at which it can close contact 0, this condition being shown by the intersection of the dashed curvewith the horizontal dashed line which represents the current required to close contact 6.

In the event, however, that the tickler contacts open for a short period of time, the relay armature will not be able to swing far enough to close c although the initial peak current is the same in both cases. Since there is ample resistance in the circuit to make it nonoscillatory, the etfect of the inductance of the relay and wiring will be to round off the sharp peaks of current but this effect will be small as compared to the inertia lag of the relay armature.

For a more complete understanding of the operation of the system of the present invention reference is again made to the complete electrical system shown in FIG. 2 of the drawings. Let it be assumed, for the purpose of description, that the mine 10 has been launched into a body of water and has come to rest on the bed thereof. Let it be assumed further that me extender mechanism 25 has operated and moved the detonator 26 into operative relation with the booster charge 24.

After an interval of time has elapsed, during which a salt washer comprising an element of the clock mechanism 29 is dissolved, a water hydrostat comprising another element of the clock mechanism 29 is caused to operate by the pressure of the surrounding Water thereby to cause the plunger 65 to he moved .out of engagement with the spring 66. When this occurs, the operation of a spring wound motor 67 is initiated, which motor drives a cam 68 of the clock mechanism in a well known manher. The cam 68 is mounted for rotation on a pivot 69 and moves in the direction of arrow '71 until the cam engages a stop pin 72 disposed within an arcuate slot 73 provided in the cam. During this movement of the cam 68, several pairs of electrical contacts included in the clock mechanism are adapted tobeclosed in sequence. Each of the several pairs of contacts comprises a follower 74 of any suitable insulating material,

which follower is urged into engagement with a cylindrical cam surface 75 provided on the cam 68. The cam surface is provided with a plurality of peripheral identations 76, 7'7, '78 therein, which indentations are adapted to'receive the followers 74 and are of varying lengths, thereby to cause the pairs of contacts to close in sequence.

According to the foreging arrangement, contacts 79 and 81 of the clock mechanism 29 are the first to close and after a predetermined interval of time, contacts 82 and 83 are closed whereupon current is caused to flow from the positive terminal of battery BA over con.- ductor 84, contacts '79 and 81 of the clock mechanism 29, conductor 57, resistor R1, conductor 58, condenser C1, conductor 59, operating magnet OM' of relay R, conductor 61, resistor R3, conductor 62, contacts 82 and 33 of the clock mechanism 29, conductor 85 from whence the circuit is completed to the negative terminal of battery BA, thereby causing the potential across condenser C1 to build up in a well known manner. The condenser potential will increase to a value corresponding to ap- After a further predetermined interval of time contacts 7 85 and 87 of the clock mechanism 29 are closed, thereby connecting one terminal of the detonator 26 to the positive terminal of battery BA. The mine is now armed and ready to respond to a vessel passing within the zone of receptivity thereof.

As a vessel moves within the zone of receptivity of the mine and thereafter approaches the mine, a wide band sound is emitted from the vessel, which sound is strongly modulated by the vessels propeller blade frequency. The intensity of such a wide band sound is of relatively small value in the area ahead of the vessel, increasing somewhat as the bow thereof passes over the mine and thereafter increasing progressively until the ships propeller is directly above the mine. The effect of this gradually increasing wide-band sound on the tickler 45 is to cause the contacts 48 and 49 thereof to be set into vibration, the contacts remaining largely closed, opening on the average for infrequent intervals corresponding to a short time T1 and a long closed time T2 as the vessel approaches the mine. When the vessel passes over the mine, the open time T1 progressively increases while the closed time T2 decreases, a definite relation existing therebetween as heretofore dcscribed.

For the purpose of description, let it be assumed that a vessel approaches the mine and transmits sound signals through the surrounding water of such a character as to 1 1 cause the contacts 48 and 49 to respond in the manner shown in the dashed curve of FIG. 6 of the drawings. When the tickler contacts 48 and 49 are initially set into vibration in response to sound signals emitted by the approaching vessel, the contacts open time T1 is very short as compared to the closed time T2, thereby causing any potential or charge attained by the condenser C1 during the short open time to be lost through the discharge circuit of condenser C1 during the longer closed time T2, the net potential remaining across C1 being that of the quiescent voltage thereof, Eq.

However, as the vessel continues to approach the mine and begins to pass over the mine, the response to the tickler contacts, defined as the ratio of T1 to T2, is such as to cross the threshold curve shown in the solid curve of FIG. 6. For the purpose of description, let it be assumed further that at this intersection, the contacts 48 and 49 open and close at intervals T1, .05 second and T2, 0.2 second, respectively.

As the contacts 48 and 49 first open for an interval of .05 second, current is caused to flow through the charging circuit of condenser C1, which is traced over the following path: positive terminal of battery BA, conductor 84, contacts 79 and 81 of the clock mechanism 29, conductor 57, resistor R1, conductor 58, condenser C1, conductor 59, operating magnet OM of relay R, conductor 61, resistor R3, conductor 62, contacts 82 and 83 of the clock mechanism 29, conductor 85 from whence the circuit is completed to the negative terminal of battery BA, thereby increasing the potential across condenser Cl a certain value in excess of Eq in a Well known manner. The direction and magnitude of this current flow is shown in FIG. of the drawings and although the magnitude of this current is sufficient to cause the armature 51 of relay R to move into engagement with the 0 contact thereof, the armature will not deflect to the 0 contact during an open interval of .05 second due to the inherent inertia and inductance lag thereof, as heretofore described.

At the end of the first open time interval T1, the potential existing across condenser C1 is shown graphically in FIG. 4 as Y1. As the contacts 48 and 49 close and thereby initiate a closed interval T2 of 0.2 second, condenser Cl begins to discharge over the following path: positive plate of condenser C1, conductor 58, resistor R2, conductor 88, contacts 48 and 49 of the chatter switch 45, conductor 61, operating magnet OM of relay R, conductor 59 from whence the circuit is completed to the negative plate of condenser C1, thereby causing the potential across condenser C1 to decrease. This decrease in condenser potential during the first T2 is also shown in FIG. 4 and by reason of the magnitude of resistor R2 and the interval of time T2, the rate and amount of potential decrease is controlled such that at the end of T2, a potential will exist across C1 which will be in excess of the quiescent potential thereof, Eq. It is apparent that the current which flows through the discharge path of condenser C1 passes through the operating magnet OM of relay Rina direction opposite to that of the current which flows therethrough when the condenser charges whereby the armature 51 of the relay is caused to move toward the 1 contact thereof. However, the magnitude of the current which flows as condenser C1 initially discharges is insufficient to close the 1 contact.

This cycle of operations continues as the vessel moves over the mine until a limiting condenser potential has been reached as shown in FIG. 4 and as heretofore described. When this occurs, the discharge potential of condenser C1 during T2 is sufficient to cause enough current to flow through the discharged path thereof for a sufficient period of time to cause the-armature 51 of relay R to move into engagement with the 1 contact thereof. When the firing contact f is closed, a circuit is completed from the positive terminal of battery BA over conductor 84, contacts 87 and 86 of the clock mechanism'29, conductor 89, electroresponsive detonating device 26, conductor 91, ,fcontact and armature 51 of relay R, conductor 61, resistor R4, conductor 92, armature 53 and cold contact 54 of the thermal delay switch 52, conductor 62, contacts 82 and 83 of the clock mechanism 29, conductor from whence the circuit is completed to the negative terminal of battery BA, thereby detonating and exploding the mine 10 beneath a vulnerable portion of the vessel. It will be understood that when current flows through resistor R4, a voltage is developed thereacross which is effective to maintain the operation of the relay, thereby to maintain the armature thereof in locked engagement with its f contact.

Whereas in the foregoing description it was assumed that the tickler contacts 48 and 49 opened at regular intervals, it will be understood that such an assumption is not necessary for satisfactory operation of the system. From the threshold curve shown in solid outline in FIG. 6, it is apparent that if the contacts 48 and 49 continue to vibrate at values of T1 and T2 which lie in the region between the threshold curve and the horizontal axis, contact 1 of relay R will eventually be closed. Similarly, if a vessel moves within the receptivity zone of the mine but does not pass over or very near the mine, the response of the tickler contacts to sound signals emanating therefrom will follow the dashed locus curve of FIG. 6 but will reach a point on the curve where T1 is largest in value and reverse therefrom back along the curve, such point lying in the region where the 1 contact of relay R will not close.

In the event a countermine shock is received by the tickler 45, the contacts 48 and 49 thereof are forced open and remain open for a relatively long period of time. When this occurs, current is caused to flow through the charging circuit of condenser C1 and hence through the operating magnet OM of relay R. In any contact open time the current flowing in the charging circuit of condenser C1 is suflicient to close the countermining contact c of relay R but the current must flow for a period of time sufiicient to allow the deflection of the armature 51 of relay R to catch up with the average current. Since a countermine shock forces the contacts 48 and 49 of the tickler to remain open for a relatively long period of time, the armature 51 is caused to move into engagement with the c contact thereof.

When this occurs a circuit is closed from the negative terminal of battery BA1 over conductor 93, contact 0 and armature 51 of relay R, conductor 61, resistor R4, conductor 92, heater coil 56 of the thermal delay switch 52, conductor 94 from whence the circuit is completed to the positive terminal of battery BA1, thereby locking up the c contact by reason of the potential drop across the resistor R4. As current continues to flow through the heater coil 56 of the thermal delay switch 52, the armature 53 thereof is-caused to move in a well known manner from the cold contact 54 thereof to the hot contact 55, such movement being accomplished in a predetermined period of time.' As the armature 53 of the delay switch 52 moves into engagement with the hot contact 55 thereof, a circuit is closed from the negative terminal of battery BA1 over conductor 93, countermining contact 0 and armature 51 of relay R, conductor 61, hot contact 55 and armature 53 of the switch 52, conductor 92, heater coil 56 of the switch 52, conductor '94 from whence the circuit is completed to the positive terminal of battery BA1, thereby short-circuiting the resistor R4 and releasing the 0 contact of relay R. When the c contact is released, current no longer flows through the heater coil 56 of the switch 52, thereby causing the armature 53 to gradually move toward the cold contact 54 thereof and to move into engagement therewith at the end of a predetermined interval of time.

It will be understood that the interval of time required for the armature of the delay switch to move from the hot contact to the cold contact thereof provides an additional delay since the detonator 26 cannot fire until the cold connection is remade. During the return of the armature of the, delay switch to the cold contact thereof, the anti-countermining cycle again may be initiated by the closure of contact of relay R notwithstanding that the detonator 26 cannot fire. Since several seconds are required for the armature of the delay switch to return to the cold contact thereof, any reverberations from a countermine shock received just before the armature of relay R is released from the 0 contact thereof, which might cause the firing contact f of relay R to be closed, will have ceased before the col connection of the delay switch is remade. This action prevents a spurious firing operation of the system due to any combination of countermining explosions.

From the foregoing it should now be apparent that an acoustic mine firing control system has been provided which is well adapted to fulfill the aforesaid objectsof the invention. While the invention has been described with particular reference to an example thereof which gives satisfactory results, it will readily be apparent to those skilled in the art to which the invention appertains,

after understanding the invention herein described, that further embodiments, modifications and changes may be made without departing from the spirit and scope thereof, as defined by the claims appended hereto.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America without payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

' 1. In a mine of the character disclosed, a mine firing circuit, energy storing means, a charging and a discharge path for said energy storing means, apair of contacts adapted to be vibrated, means responsive to sound signals transmitted through the surrounding water and adapted to cause said pair of contacts to open and close for vari-' able intervals of time in accordance with the character of the sound signalsreceived by the sound responsive means, means including said pair of contacts for causing ,current to flow through said charging path when the con- (acts are open, means also including said pair of contacts and said energy storing means for causing current to flow through said discharge path when the contacts are closed, and an eiectro-responsive device controlled by the current in said discharge path and adapted to close said firing circuit when the ratio of discharge current to charging current is Within a predetermined ratio range.

2. In an acoustic mine firing control system, the combination of a mine firing circuit, vibration responsive means, energy storing means, means including said vibration responsive means adapted to cause energy to be stored in and discharged from said energy storing means alternately in a manner corresponding to the character of vibrations received by the vibration responsive means, and means controlled by said discharged energy for closing said mine firing circuit when the flow of discharge energy is of predetermined character.

3. In a vibrationally controlled underwater mine adapted .to be fired in response to vibrations of predetermined character transmitted through the surrounding Water for a predetermined period of time by an approaching vessel, a mine firing circuit, a vibration responsive device, energy storing means, circuit means including a pair of contacts controlled by said vibration responsive device for causing energy to be stored gradually in said energy storing means until a predetermined amount of energy has been stored therein and thereafter to discharge said predetermined amount of energy therefrom, an electro-responsive device adapted to close said firing circuit, and means for causing said electro-responsive device to be operated when said predetermined amount of energy is discharged therethrough.

4. In a marine mine of the character disclosed, a mine firing circuit, an energy responsive device adapted to be operated to close said firing circuit when energy is caused to flow through said device at a predetermined rate and for a predetermined period of time, two control circuits including means for energizing said energy responsive device, a sound responsive device having circuit controlling .means adapted to cause energy to flow through said control circuits alternately when sound signals are received by the sound responsive device, and means including said circuit controlling means for controlling the rate and time of energy flow through said control circuits in accordance with the character of sound signals received .by the sound responsive means whereby the electro responsive device is operated While signals of predetermined character are being received by the sound responsive device.

5. An acoustic mine firing control system comprising in combination, a mine firing circuit, an electro-responsive device adapted to sheet operation of said mine firing circuit as the device is operated, two control circuits including said device and adapted to effect operation thereof when the device is transferred to and from said control circuits alternately in a predetermined manner, and a sound responsive device including means adapted to transfer control of said electro-responsive device between said control circuits alternately in said predetermined manner while sound signals of predetermined character are being received by the sound responsive device.

6. An acoustic mine firing control system comprising, in combination, an electro-responsive device adapted to be operated variably in accordance with the character of the energy flowing therethrough, two control circuits including said electro-responsive device and energizing means therefor, means responsive to sound signals for causing energyto flow through said control circuits selectively in a predetermined manner in accordance with sound signals of predetermined character received by the sound responsive means, a mine firing circuit, and a mine sterilizing circuit, said electro-responsive device having circuit closing means adapted to close said firing and sterilizing circuits selectively as the electro-responsive device is operated in accordance with said predetermined energization of a selected control circuit.

7. In an acoustic mine firing control system, the combination of energy storing means, vibration responsive means, means including said vibration responsive means and adapted to cause energy to be stored in and discharged from said energy storing means alternately in a manner corresponding to the character of vibrations received by the vibration responsive means, means for producing a firing actuation of said system, means for preventing a firing actuation of said system, and means responsive to said stored and said discharged energy for initiating the operation of said firing and said preventing means selectively in accordance with the character of the stored and discharged energy.

8. In a mine of the character disclosed, a mine firing circuit, a mine sterilizing circuit, an energy responsive device adapted to be operated to close said circuits selectively in accordance with the direction, rate and time of energy flow therethrough, and circuit means including a sound responsive device and adapted to cause energy to flow through said energy responsive device in a direction, at a rate and for a period of time sufiicient to effect said operation thereof while sound signals of predetermined character are being received by the sound responsive device.

9. In a marine mine of the character disclosed, in combination, a sterilizing circuit therefor, a firing circuit therefor, circuit closing means associated with both said sterilizing circuit and said firing circuit and adapted to close said circuits selectively, and means responsive to sound signals received through the surrounding water for causing said circuit closing means to close said circuits selectively in accordance with the character of the signals received.

10. In a mine of the character disclosed, a firing circuit therefor, a sterilizing circuit therefor, a relay having means for closing said firing and said sterilizing circuits selectively as the relay is operated selectively, a sound responsive device, a pair of contacts adapted to be vibrated by said sound responsive device while sound signais are received thereby, and circuit means including said pair of contacts for causing said relay to be operated to close said firing circuit while the contacts vibrate in a predetermined manner in response to sound signals of predetermined character received by the sound responsive device or selectively for causing the relay to be operated to close said sterilizing circuit While the contacts vibrate in a different manner in response to sound signals of difierent character received by the sound responsive device.

11. In an acoustic mine firing control system, the combination of a mine firing circuit, an energy storage device, means responsive to sound signals, means including said sound responsive means for causing a predetermined amount of energy to be stored gradually in said energy storage device when sound signals of predetermined character are received by the sound responsive means and thereafter causing said energy to be dis charged therefrom, means controlled by said discharged energy for closing said firing circuit, normally inactive means for preventing a closure of said firing circuit for a predetermined interval, and means including said sound responsive means and said circuit closing means for initiating the operation of said closure preventing means when sound signals of predetermined character and of different character are received concurrently by the sound responsive means.

12. In an acoustically controlled marine mine adapted to be fired in response to sound signals received from an approaching vessel, a mine firing circuit having means for firing the mine when the firing circuit is closed, a sensitive relay, said relay having a contact element movable fnom an initial unoperated position to a circuit closing position for closing the mine firing circuit as the relay operates, energy storing means adapted to operate said relay when a predetermined amount of energy has been stored therein, a pair of contacts adapted to be vibrated, sound responsive means adapted to cause said contacts to open and close vibrationally for intervals of time as the vessel enters the threshold of sensitivity of the mine and continues to approach the mine, and means including said pair of contacts for causing said predetermined amount of energy to be stored gradually in said energy storing means when the ratio of open to closed intervals of the contacts during continuous vibration thereof is Within a predetermined ratio range.

13. In a system for firing a mine disposed within a body of water, a condenser, a source of power, electroresponsive detonating means adapted to fire the mine when said source of power is connected thereto, a relay in circuit with said condenser, said relay having a contact element movable from an initial unoperated position to a circuit closing position for connecting said detonating means to the source of power as the relay operates in response to a fiow of current impulses therethrough of predetermined character, and means responsive to sound signals transmitted through the surrounding Water and having means adapted to cause said predetermined current impulses to flow through said condenser and said relay while sound signals of predetermined character are being received by the sound responsive means.

14. In an acoustically controlled underwater mine adapted to be fired in response to sound signals received from an approaching vessel, a pair of contacts adapted to be vibrated, a sound responsive device for causing said contacts to vibrate in a predetermined manner in response to sound signals of a predetermined character received by the device as the vessel enters the threshold of sensitivity ofthe mine, a mine firing circuit, a relay, a contact element on said relay and movable from an initial un- 'operatedposition to a circuit closing position, closing said mine firing circuit, and means including said pair of con- 1 tacts for causing said'relay to move said contact element to said circuit closing position gradually as the vessel enters the threshold of sensitivity of the mine, whereby said firing circuit is closed as the vessel moves within the zone of destructivity of the mine.

15. In a mine of the character disclosed, a circuit for disarming the mine for a predetermined interval comprising, an electro-responsive timing device having a pair of contacts and an armature movable from a first contact to the other of said pair of contacts gradually while the disarming circuit is closed and movable gradually back. to the first contact when the circuit thereafter is opened, means for closing said disarming circuit, means controlled by sound signals of predetermined character for initiating the operation of said circuit closing means, means included in said disarming circuit for locking up said circuit closing means for a predetermined period of time when the disarming circuit is closed, and a mine firing circuit including said armature and said first contact and adapted to be disarmed when the armature is moved out of engagement with the first contact.

16. In an acoustic mine firing control system, the combination of a mine firing circuit having energy storing means therein, means including a vibration responsive device constructed and arranged to cause energy to be stored in and discharged from said energy storing means alternately in a manner corresponding to the character of vibrations received by the vibration responsive device, and means controlled by said discharged energy for closing said mine firing circuit when the flow of discharge energy is of predetermined character.

17. In a vibrationally controlled underwater mine to be fired in response to vibrations of predetermined character transmitted through the surrounding water for a predetermined period of time by an approaching vessel, a vibration responsive device, energy storing means, a mine firing circuit having circuit control means therefor, said circuit control means including a pair of contacts controlled by said vibration responsive device for causing energy to be stored gradually in said energy storing means until a predetermined amount of energy has been stored therein and thereafter to discharge said predetermined amount of energy therefrom, and means including an electro-responsive device constructed and arranged to close said firing circuit as the electro-responsrve device is operated in response to said predetermined amount of discharged energy.

18. In a marine mine of the character disclosed, a mine firing circuit, an energy responsive device constructed and arranged to close said firing circuit when energy is caused to flow through said device at a predetermined rate and for a predetermined period oftime, two control circuits, means for energizing said energy :responsive device, a sound responsive device, circuit control means operatively connected to said sound responsive device constructed and arranged to cause energy to flow through said control circuits alternately in response to sound signals received by the sound responsive device, and means including said circuit controlling means for controlling the rate and time of energy flow through said control circuits in accordance with the character of sound signals received by the sound responsive means whereby the electro-responsive device is operated as signals of predetermined character are being received by flow through said control circuits alternately when sound signals are received by the sound responsive device, and

means including said circuit controlling means for con- References Cited in the file of this patent UNITED STATES PATENTS Heap et a1. July 22, Hammond Feb. 21, Dufiie May 19, Hammond Dec. 27, 

